Various methods for cleaning up sites contaminated with immiscible fluids, such as solvents, gasoline, diesel fuel and oils, include partial, in situ removal of the fluid from the earth's subsurface. Current methods include boring a well into the subsurface and either recovering a fraction of the spilled fluid by skimming, or pumping groundwater out from below the spilled fluid to cause some portion of the fluid to collect in previously uncontaminated regions and then pumping the fluid out. In another method, the fluid is intercepted in a trench or drain constructed at a level below the spilled fluid. These methods are typically ineffective, cause further spread of the contaminants through the subsurface of the soil, and result in a large portion of the fluid remaining trapped in soil and groundwater.
One method which uses vacuum extraction for removal of volatile contaminant from soil is described in U.S. Pat. No. 4,660,639. The method relies on the placement of alternating layers of high and low permeability filler in an annulus between a well bore and well pipe to cause movement of air through contaminated soil toward the well. This method does not provide means for adjustment of the air path and does not provide for removal of relatively less volatile components (i.e., semi-volatile and non-volatile components).
Another method uses vacuum extraction along with a series of air injection wells. This method, described in U.S. Pat. No. 4,730,672, does not provide means for adjustment of either the vacuum draw or the air injection in order to adjust the air path in the subsurface. This method does not provide for removal of relatively less volatile components.
The methods of both U.S. Pat. Nos. 4,660,639 and 4,730,672 are limited to removal of contaminants from a vadose zone, the upper, unsaturated layer of subsurface. Thus, these methods do not address clean-up of lower layers, such as a groundwater zone.
Therefore, what is needed is a method which removes volatile, semi-volatile and non-volatile components of spilled fluid from both the vadose and groundwater of the subsurface of earth, in situ, while preventing the spread of the spill and which selectively and adjustably applies vacuum draw to one or more contaminated layers of the subsurface.